Synthesis of swainsonine and analogs thereof

ABSTRACT

Swainsonine and analogs, namely 1,4-dideoxy-1,4-imino-D-mannitol and the novel ring contracted swainsonines, Δ(1S,2R,7R,7aR)-1,2-trihydroxypyrrolizidine and (1S,2R,7S,7aR)-1,2,7-trihydroxypyrrolizidine, are synthesized from the divergent intermediate, 4,5-anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-D-talitol. These novel compounds are glycosidase inhibitors.

This is a division of application Ser. No. 07/424,628, filed Oct. 20,1989 now U.S. Pat. No. 5,023,340.

BACKGROUND OF THE INVENTION

This invention relates to the syntheses of swainsonine and analogsthereof.

Swainsonine (1), a potent and specific inhibitor of lysosomal and someof the processing forms of α-mannosidase [Cenci di Bello et al.,Biochem. J. 215, 693 (1983); Tulsiani et al., J. Biol. Chem. 257, 7936(1982)], may have therapeutic value as an antimetastic [Humpheries etal., Cancer Res. 48, 1410 (1988)], and tumor-proliferative [Dennis,Cancer Res. 46, 5131 (1986)], or immunoregulatory agent [Kino et al., J.Antibiot. 38, 936 (1985)]. Studies on the inhibition of humanα-mannosidase by swainsonine analogs such as1,4-dideoxy-1,4-imino-D-mannitol (DIM) (2) [Fleet et al., J. Chem. Soc.Chem. Commun. 1984, 1240; Palamarczyk et al., Arch. Biochem. Biophys.243, 35 (1985); Daniel et al., Glycoconjugate J. 6, 229 (1989)] haverecently been reported [Cenci di Bello et al., Biochem. J. 259, 855(1989)]. N-Alkylation of open chain swainsonine analogues effectivelyremoves all ability to inhibit α-mannosidase [Al Daher et al., Biochem.J. 258, 613 (1989)]; it is therefore of interest to determine the effectof variation of the size of the six-membered ring of swainsonine on theinhibition of mannosidases. There has been much interest in thesynthesis of swainsonine [Bashyal et al., Tetrahedron 43, 3083-3093(1987); Dener et al., J. Org. Chem. 53, 6022 (1988), and referencescited therein], and, in particular, in procedures that could producesignificant quantities of material [Bennett et al., J. Am. Chem. Soc.111, 2580 (1989)].

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the present invention, a novel method for thesyntheses of swainsonine and analogs thereof from mannose is provided.By this method4,5-Anhydro-1-azido-1-deoxy-2,3-O-isopropylident-D-talitol (6) is usedas a divergent intermediate for the efficient and practical syntheses of1,4-dideoxy-1,4-imino-D-mannitol (2), swainsonine (1) and of the ringcontracted swainsonines, (1S, 2R, 7R, 7aR)-1,2,7-trihydroxypyrrolizidine(3) and (1S, 2R, 7S, 7aR)-1,2,7-trihydroxypyrrolizidine (4). The lattercompound (4) is structurally related to the pyrrolizidine alkaloid1,7a-diepialexine (5), recently isolated from Castanospermum australeand demonstrated to be a powerful amyloglucosidase inhibitor [Nash etal., Phytochemistry, In Press 1989].

The ring contracted swainsonines (1S, 2R, 7R,7aR)-1,2,7-trihydroxypyrrolizidine (3) and the 7S-epimer (4), are novelcompounds and inhibitors of glycosidases but have weaker such activitythan swainsonine.

Syntheses of 1,4-dideoxy-1,4-imino-D-mannitol (2), swainsonine (1) andthe ring contracted swainsonines (3) and (4) from the divergentintermediate, 4,5-anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-D-talitol(6), is preferably carried out by the stepwise method as follows inwhich compound numbers in parentheses correspond to compounds shown bychemical structure herein:

Synthesis of 1,4-Dideoxy-1,4-Imino-D-Mannitol

a) 4,5-Anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-D-talitol (6) iscatalytically hydrogenated, e.g. in the presence of palladium on carbon,to provide ring closure and give the protected pyrrolidine (13), and

b) The isopropylidene protecting group in the protected pyrrolidine (13)is removed by acid hydrolysis to give 1,4-dideoxy-1,4-imino-D-mannitol.

Syntheses of Swainsonine

a) 4,5-Anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-D-talitol (6) isesterified at the primary hydroxyl with triflic anhydride to give thetriflate (9),

b) The triflate (9) is reacted with lithium tert-butyl acetate to givethe chain extended azidoester (14),

c) The azidoester (14) is catalytically hydrogenated, e.g. withpalladium on carbon, to give the aminoester (16),

d) The aminoester (16) is heated with sodium methoxide to provide ringclosure and give the δ-lactam (17),

e) The δ-lactam (17) is reduced with borane:dimethyl sulfide to give theaminoborane adduct or complex (18) and

f) The isopropylidene protecting group in aminoborane adduct (18) andthe borane group are removed by acid hydrolysis to give the desiredswainsonine (1).

Synthesis of (1S,2R,7R,7aR)-1,2,7-Trihydroxypyrrolizidine (3)

a) Triflate (9) is reacted with lithium cyanide to form theazidocyanoepoxide or nitrile (15),

b) The azidocyanoepoxide (15) is catalytically hydrogenated, e.g. withpalladium on carbon, to give the amine (19),

c) Protection of the nitrogen on amine (19) is carried out by reactionwith benzyl chloroformate to give the benzyloxycarbonyl derivative (20),

d) The benzyloxycarbonyl derivative (20) is partially hydrolyzed at thenitrile group by hydrogen peroxide to give the amide (21),

e) The amide (21) is silylated to give the protected amine (22),

f) The benzyloxycarbonyl protecting group is removed by acid hydrolysisof the protected amine (22) to give the aminoamide (23),

g) The aminoamide (23) is treated with sodium hydrygen carbonate to givethe silyl alcohol or lactam (24),

h) the lactam (24) is treated with borane:dimethyl sulfide complex toafford the amine borane adduct (26), and

i) The isopropylidene and silyl protecting groups and the borane groupin the amine borane adduct (26) are removed by acid hydrolysis to givethe desired ring contracted swainsonine,(1S,2R,7R,7aR)-1,2,7-trihydroxypyrrolizidine (3).

Synthesis of (1S,2R,7S,7aR)-1,2,7-Trihydroxypyrrolizidine (4)

a) The silyl alcohol or lactam (24) is reacted with fluoride ion toremove the silyl protecting group and give alcohol (25),

b) The alcohol (25) is oxidized, e.g. with pyridinium chlorochromate, togive the corresponding ketone (28),

c) The ketone (28) is reduced, e.g. with sodium borohydride, to give theinverted alcohol or lactam (29),

d) The lactam (29) is reduced with borane:dimethyl sulfide complex toafford the borane adduct (27), and

e) The isopropylidene protecting group and the borane group in boraneadduct (27) are removed by acid hydrolysis to give the desired ringcontracted swainsonine, (1S,2R,7S,7aR)-1,2,7-trihydroxypyrrolizidine(4).

Other such suitable reactants for use in the foregoing syntheses of1,4-dideoxy-1,4-imino-D-mannitol (2), swainsonine (1) and the ringcontracted swainsonines (3) and (4) will be apparent to the personskilled in the art after reading the present disclosure. These reactantsare generally used in proportions such as to satisfy the stoichiometryof the above reaction steps. Illustrative of suitable reactants are theuse of a noble metal catalyst such as platinium or palladium on carbonfor the catalytic hydrogenation; use of tert-butyldimethylsilyl chlorideor tert-butyldiphenylsilyl chloride to introduce the silyl protectinggroups; use of hydroxyl protecting groups such as isopropylidene orcyclohexylidene; use of tetrabutylammonium fluoride to remove the silylprotecting groups; use of trifluoroacetic acid for the hydrolyticremoval of protecting groups; and use of organic solvents such asdioxane, DMF, THF, DMSO, N-methylpyrrolidine, acetonitrile and the likeas solvent media for the reaction steps.

DETAILED DESCRIPTION OF THE INVENTION

The invention is conveniently illustrated by the following descriptionof the preferred embodiments in which4,5-Anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-D-talitol (6) isderived from mannose by introduction of an azido group at C-1 and by asingle inversion at C-4 and then used as a readily available divergentintermediate for the synthesis of the desired swainsonine and analogsthereof. The synthesis of all these synthetic compounds requires theintroduction of nitrogen at C-4 of mannose with overall retention, thatis double inversion, of configuration. The dimesylate (10), readilyavailable on a large scale from mannose in an overall yield of 80%[Fleet et al., Tetrahedron 44, 2649 (1988)], undergoes selectivedisplacement of the primary mesylate by sodium azide inN,N-dimethylformamide:water to give the azidomesylate (11), [62% yield;87based on recovered (10)] which, on partial hydrolysis in aqueousmethanol with camphor sulphonic acid, affords the diol (12), m.p.82°-84° C., [α]_(D) ²⁰ +90.8° (c, 0.51 in CHCl₃) in 56% yield [81% basedon unrecovered dimesylate (10)]. Treatment of (12) with saturatedmethanolic barium methoxide [Kusman and Kiss, Carbohydr. Res. 153, 45(1986) and references cited therein] gave the azido epoxide (6) in 95%yield. The azidoepoxide (6) is moderately unstable at room temperatureand the material was used immediately; (6) was fully characterized asthe stable tert-butyldimethylsilyl (7) and tert-butyldiphenylsilyl (8)ethers. ##STR2##

Hydrogenation of the azide (6) in 1,4-dioxane:water in the presence ofpalladium on carbon gave the protected pyrrolidine (13), m.p. 86°-88° C.[lit. 86°-88° C.] in 90% yield [31% overall yield from mannose; 45% fromdiacetone mannose]; removal of the isopropylidene protecting group from(13) by aqueous trifluoracetic acid, followed by conversion to thehydrochloride salt, afforded DIM (2) as the hydrochloride, m.p.149°-151° C. [lit. m.p. 148°-149° C.], identical to authentic material[Bashyal et al., Tetrahedron Lett. 28, 4189 (1987)]. ##STR3##

The two carbon extension for the synthesis of swainsonine was achievedby initial esterification of the primary alcohol bytrifluoromethanesulphonic anhydride to give the triflate (9) which wasreacted with lithium tert-butyl acetate in tetrahydrofuran to give thechain extended ester (14), an oil, [α]_(D) ²⁰ +63.5° (c, 0.98 in CHCl₃)in 60% overall yield from the azidomesylate (12). Hydrogenation of theazidoester (14) in ethanol with palladium on carbon as the catalyst gavethe aminoester (16) (80% yield) which on heating with sodium methoxidein methanol gave the δ-lactam (17), m.p. 126°-128° C. [lit. * m.p.125°-127° C.], in 92% yield. [*Setoi et al., J. Org. Chem. 30, 3948(1985)]. Reduction of the lactam (17) by borane:dimethyl sulphide gavethe non-polar borane adduct (18) [70% yield] which was easily purifiedby flash chromatography; treatment of (18) with aqueous trifluoroaceticacid gave, after purification by ion exchange chromatography,swainsonine (1), m.p. 126°-128° C. [lit. m.p. 125°-127° C.], in 86%yield [12% from mannose; 18% from diacetone mannose], identical to anauthentic sample. Satisfactory spectral data were obtained for all newcompounds disclosed herein; correct CHN microanalytical data wasobtained for compounds (3), (4), (7), (8), (12), (13), (14), (17), (19),(20), (21), (22), (24), (25), and (29). For (6), δ_(C) (CDCl₃): 110.0(s), 76.54 and 76.44 (2d, C-2 and C-3), 60.8 (t, C-6), 56.7 and 52.3(2d, C-4 and C-5), 50.3 (t, C-1), 27.2 and 24.7 (2q).

The synthesis of the ring contracted swainsonines requires a one carbonextension of the azidotriflate (9). Treatment of (9) with lithiumcyanide resulted in the formation of the nitrile (15) [77% yield from(12)]; the use of lithium cyanide in this displacement is critical[Harusawa et al., Tetrahedron Lett. 28, 4189 (1987)]. Hydrogenation of(15) in ethanol with a catalyst of palladium on carbon gave (19), m.p.92°-92° C., [α]_(D) ²⁰ -77.2° (c, 0.32 in CHCl₃) in 73% yield.Protection of the nitrogen as the benzyloxycarbonyl (Z) derivative (20),followed by partial hydrolysis of the nitrile by hydrogen peroxide inmethanol in the presence of hexene gave the amide (21) which wassilylated to (22) and the Z-protecting group removed to give (23), m.p.143°-144° C., [α]_(D) ²⁰ -55.0° (c, 0.26 in CHCl.sub. 3) [75% yield from(19)]. Treatment of the aminoamide (23) with a suspension of sodiumhydrogen carbonate in carbon tetrachloride gave the lactam (24), m.p.106°-109° C. (92% yield) which on treatment with borane:dimethylsulphide afforded the amine borane adduct (26) (70% yield) which withaqueous trifluoroacetic acid and purification by ion exchangechromatography gave the ring contracted swainsonine (3), m.p. 150°-153°C., [α]_(D) ²⁰ -29.3° (c, 0.15 in MeOH) [68% yield]. ##STR4##

The epimeric trihydroxypyrrolizidine (4) was obtained by inversion ofthe free hydroxy group in (25), m.p. 148°-149° C., [α]_(D) ²⁰ 0° (c,0.30 in CHCl₃), prepared by the removal of the silyl protecting group in(24) by fluoride (100% yield). Oxidation of (25) by pyridiniumchlorochromate gave the ketone (28) which, on treatment with sodiumborohydride in ethanol, cleanly gave the inverted alcohol (29), m.p.132°-134° C., [α]_(D) ²⁰ -19.3° (c, 0.46 in CHCl₃), [94% yield from(25)]. Reduction of lactam (29) with borane:dimethyl sulphide affordedthe borane adduct (27) (72% yield) which with aqueous trifluoroaceticacid and purification by ion exchange chromatography gave (4). m.p.125°-127° C., [α]_(D) ²⁰ -6.9° (c, 0.13 in MeOH), in 70% yield. For (3),δ_(C) (D₂ O): 73.74 and 73.14 (2d, C-1 and C-2), 70.9 (d, C-7), 70.6 (d,7a), 56.0 (d, C-3), 53.5 (t, C-5 ), 34.8 (t, C-6). For (4), δ_(C) (D₂O): 73.14 (d, C-1 and C-2), 72.8 (d, C-7), 68.0 (d, C-7a), 57.3 (d,C-3), 53.5 (t, C-5), 35.6 (t, C-6).

The effects of the ring contracted swainsonines (3) and (4) on theinhibition of 14 human liver glycosidases was studied by the assaymethods described in Palamarczyk et al., Arch. Biochem. Biophys. 243, 35(1985); Daniel et al., Glycoconjugate J. 6, 229 (1989) and Cenci diBello et al., Biochem. J. 259, 855 (1989). The pyrrolizidine analog ofswainsonine (3) is a weak inhibitor of lysosomal α-mannosidase (I₅₀1.5×10⁻³ M) compared with swainsonine (1) (Ki 7×10⁻⁸ M); (3) is alsoless effective in inhibiting the Golgi II and neutral processingmannosidases. At a concentration of 1 mM (3) also inhibited theβ-galactosidase by 69%, the broad specificityβ-galactosidase/β-glucosidase moderately (25%) and the α-fucosidase by33%. The inhibition of Jack bean α-mannosidase by (3) is also very weak(K_(i) 1.7×10⁻³ M) in comparison to the inhibition by swainsonine [J.Chem. Soc. Chem. Commun. 1984, pp. 1240-1241]; also no significantinhibition by (3) was observed of the following glycosidases: snailβ-mannosidase, yeast α-glucosidase, almond β-glucosidase, Aspergillusniger and green coffee bean α-galactosidases, bovine β-galactosidase,bovine kidney α-fucosidase, or bovine β-hexosaminidase.

The epimeric pyrrolizidine (4), which corresponds to 8-epi-swainsonine,does not inhibit human liver α-mannosidases but is a weak inhibitor ofthe broad specificity β-galactosidase/β-glucosidase (40%); in this (4)resembles the specificity of glycosidases shown by 8-epi-swainsonine[Cenci di Bello et al., Biochem. J. 259, 855 (1989)].

The following examples will further illustrate the invention in greaterdetail although it will be appreciated that the invention is not limitedto these specific examples. The starting dimesylate (10) was synthesizedas described by Fleet et al., Tetrahedron 44, 2649-2655 (1988), byconverting diacetone mannose into the corresponding diol,1,2:4,5-di-O-isopropylidene-D-mannitol, and then esterifying the diolwith methanesulfonyl chloride to give dimesylate (10).

Examples 1 to 3 illustrate the syntheses of the divergent intermediate,4,5-anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-D-talitol (6), from thedimesylate (10). Examples 4 and 5 illustrate the preparation of thetert-butyldimethylsilyl (7) and tert-butyldiphenylsilyl (8) ethers of(6). Examples 6 and 7 illustrate the synthesis of1,4-dideoxy-1,4-imino-D-mannitol from the divergent intermediate (6).Examples 8 to 13 illustrate the synthesis of swainsonine (1) from thedivergent intermediate (6). Examples 14 to 22 illustrate the synthesisof ring contracted swainsonine (3) starting from the epoxytriflate (9)made in the swainsonine synthesis, while Examples 23 to 27 illustratethe synthesis of ring contracted swainsonine (4), starting from thesilyl alcohol (24) made in the synthesis of the ring contractedswainsonine (3).

METHODS

Melting points were recorded on a Kofler hot block and are uncorrected.Infrared spectra were recorded on a Perkin-Elmer 297 spectrophotometeror a Perkin-Elmer 1750 FT spectrophotomether as a thin film unlessotherwise stated. ¹ H NMR spectra were run at 300 MHZ on a Bruker WH 300spectrometer (500 MHz on a Bruker AM 500 spectrometer). ¹³ C NMR spectrawere recorded on a Varian Gemini 200 (50 MHz) or a Bruker 250 (62.9 MHz)spectrometer. Multiplicities were assigned using DEPT sequence on theGemini and by off resonance decoupling on the Bruker. Spectra were runin deuteriochloroform unless otherwise stated, using residual protonatedsolvent as an internal standard. ¹³ C D₂ O spectra use 1,4-dioxane ormethanol as the internal standard. Mass spectra were recorded on VGMicromass 30F, ZAB IF or Masslab 20-250 spectrometers. Desorptionchemical ionization (DCI, NH₃) and chemical ionization (CI, NH₃)techniques were used. Optical rotations were measured on a Perkin-Elmer241 polarimeter with a path length of 1 dm. Concentrations were given ing/100 ml. Microanalyses were performed by the microanalysis service ofthe Dyson-Perrins laboratory, Oxford, U.K. Thin layer chromatography(t.l.c.) was carried out on aluminum sheets pre-coated with 60F₂₅₄silica. Plates were developed using either 5% v/v concentrated sulphuricacid in methanol, 0.2% w/v cerium (IV) sulphate and 5% ammoniummolybdate in 2M sulphuric acid or 0.5% ninhydrin in methanol. Flashchromatography was carried out using Merck Keiselgel 60 (0.04-0.063 mm).Solvents were dried according to the following procedures:Dichloromethane was refluxed over and distilled from calcium hydride.N,N-dimethylformamide was distilled under reduced pressure from calciumhydride. Methanol was distilled from magnesium methoxide. Pyridine wasdistilled from and stored over potassium hydroxide. Tetrahydrofuran wasdistilled from a purple solution of sodium benzophenone ketylimmediately before use. Hexane was distilled at 68° C. before use toremove involatile fractions. Hydrogenations were executed at atmosphericpressure of hydrogen gas maintained by inflated balloon.

EXAMPLE 11-Azido-1-deoxy-2,3:5,6-di-O-isopropylidene-4-O-methanesulphonyl-D-mannitol(11)

To the dimesylate (10) (13 g, 31 mmol) in dimethylformamide:water (9:1,130 ml) was added all at once sodium azide (6 g, 93 mmol). The reactionmixture was then stirred at 90° C. for 18 hours. T.l.c. (50%, ethylacetate/hexane) then showed starting material (R_(f) 0.35) and product(R_(f) 0.55). The solvent was then removed in vacuo to give a pale brownresidue which was taken up in ether (150 ml) and washed with water (100ml). The water was then back extracted with ether (50 ml). The combinedethereal extracts were then washed with brine (4×50 ml) before beingdried (sodium sulphate). Removal of the solvent followed by flashchromatography (0-80%, ethyl acetate/hexane) gave1-azido-1-deoxy-2,3:5,6-di-O-isopropylidene-4-O-methanesulphonyl-D-mannitol(11), (7 g, 62%) as a colourless oil. υ_(max) : 2104 cm⁻¹. ¹H NMR ∂: 4.75 (1H, t, H-4), 4.4-4.0 (5H, m, H-2, H-3, H-5, H-6, H-6'),3.5 (2H, m, H-1, H-1'), 3.17 (3H, s, SCH₃), 1.57, 1.44, 1.40, 1.36 (12H,4s, CH₃). ¹³ C NMR ∂: 110.5, 109.4 (2s, C(CH₃)₂), 78.8, 76.6, 76.2, 74.8(4d, C-2, C-3, C-34, C-5), 67.0 (t, C-6), 50.9 (t, C-1), 39.0 (q, SCH₃),27.4, 25.8, 25.5, 24.8 (4q, CH₃). m/z (DCI, NH₃): 383 (M+NH₄ ⁺, 15%),338 (M+H--N₂ ⁺, 100%). Starting dimesylate was also recovered (3.8 g,30%).

EXAMPLE 21-Azido-1-deoxy-2,3-O-isopropylidene-4-O-methanesulphonyl-D-mannitol(12)

To the azidomesylate (11) (10 g, 27.4 mmol) was added methanol:water(10:1, 33 ml), followed by camphorsulphonic acid (30 mg). The solutionwas then stirred for 2 hours at 50° C. by which time t.l.c. (50%, ethylacetate/hexane) showed the reaction to be about 30% complete. The acidwas then neutralised with 0.880 ammonia solution before the solvent wasremoved in vacuo. Preadsorption onto silica gel and purification byflash chromatography (30% ethyl acetate/hexane followed by neat ethylacetate) gave starting material and product. The recovered startingmaterial was then twice recycled by the same procedure to give1-azido-1-deoxy-2,3-O-isopropylidene -4-O-methanesulphonyl-D-mannitol(12), (5 g, 56%) m.p. 82°-84° C. (ethyl acetate/hexane). [α]_(D) ²⁰+90.8° (c, 0.51 in CHCl₃). υ_(max) : 3400, 2104 cm⁻¹. ¹ H NMR ∂: 4.80(1H, t, H-4), 4.43 (2H, m, H-2, H-3), 3.90-3.72 (3H, m, H-5, H-6, H-6'),3.54 (2H, d, H-1, H-1'), 3.18 (3H, SCH₃), 2.90 (1H, d, OH), 2.30 (1H, t,OH), 1.55, 1.41 (6H, 2s, CH₃). ¹³ C NMR ∂: 109.0 (s, C(CH₃)₂), 78.7,76.5, 71.9 (3d, C-2, C-3, C-4, C-5), 62.1 (t, C-6), 51.1 (t, C-1), 38.9(q, SCH₃), 27.4, 25.4 (2q, CH₃). m/z (DCI, NH₃): 343 (M+NH₄ ⁺, 50%), 298(M+H--N₂ ⁺, 100%), 202 (M+H--N₂ --HOSO₂ Me⁺, 40%), 142 ((202--HOCH₂CHOH)⁺, 40%). (Found C, 36.66; H, 5.83; N, 12.63%. C₁₀ H₁₉ N₃ O₇ Srequires C, 36.92; H, 5.85; N, 12.92%) and starting material (3.1 g,31%).

EXAMPLE 3 4,5-Anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-D-talitol (6)

To the diol (12) (2.88 g, 8.86 mmol) in freshly distilled, dry methanol(20 ml) was added a saturated barium methoxide solution (4 ml). Thereaction was then stirred for 30 minutes at room temperature by whichtime no starting material (R_(f) 0.2) remained and only one product(R_(f) 0.25) was visible by t.l.c. (50%, ethyl acetate/hexane). Carbondioxide (solid) was then added followed by silica gel. Removal of thesolvent in vacuo and flash chromatography (0-70%, ethyl acetate/hexane)then gave 4.5-anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-D-talitol(6), as a colourless oil (1.9 g, 95%). [α]_(D) ²⁰ +77.3° (c, 0.51 inCHCl₃).υ_(max) : 3500, 2104 cm⁻¹. ¹ H NMR ∂:4.38 (1H, m, H-2), 4.08-3.62(3H, m, H-3, H-6, H-6'), 3.54 (2H, m, H-1, H-1' ), 3.09 (2H, m, H-4,H-5), 2.30 (1H, s, OH), 1.50, 1.35 (6H, 2s, CH₃). ¹³ C NMR ∂:110.0 (s,C(CH₃)₂), 76.5, 76.4, (2d, C-2, C-3), 60.8 (t, C-6), 57.6 (d, C-5), 52.3(2d, C-4, C-5), 50.3 (t, C-1), 27.2, 24.7 (2q, CH₃). m/z (DCI, NH₃): 247(M+NH₄ ⁺, 5%), 230 (M+H⁺, 4%), 202 (M+H--N₂ ⁺, 70%), 184 (M+H--N₂ --H₂O⁺, 50%), 142 (100%).

EXAMPLE 44,5-Anhydro-1-azido-6-O-tert-butyldimethylsilyl-1-deoxy-2,3-O-isopropylidene-D-talitol(7)

To the epoxy alcohol (6) (0.4 g, 1.75 mmol) in freshly distilled, drydimethylformamide (10 ml) was added recrystallised imidazole (340 mg,5.24 mmol) and tert-butyldimethylsilyl chloride (400 mg, 2.62 mmol). Thereaction mixture was then stirred at room temperature for 12 hours. Thesolvent was then removed in vacuo and the residue taken up in diethylether (40 ml) before being washed with water (10 ml), then brine (3×15ml), dried (sodium sulphate) and purified by flash chromatography(0-20%, ethyl acetate/hexane) to give 4,5-anhydro-1-azido-6-O-tert-butyldimethylsilyl-1-deoxy-2,3-O-isopropylidene-D-talitol (7),as a colourless oil. (0.54 g, 90%). +51.8° (c, 1.2 in CHCl₃). υ_(max) :3500, 3019, 2107 cm⁻¹. ¹ H NMR ∂:4.37 (1H, m, H-2), 3.90 (1H, dd, H-6),3.86 (1H, t, H-3), 3.66 (1H, dd, H-6'), 3.54 (2H, m, H-1, H-1'), 3.03(1H, quin., H-5), 2.95 (1H, dd, H-4), 1.49, 1.34 (6H, 2s, CH₃), 0.87(9H, s, C(CH₃)₃), 0.04 (6H, s, SiCH₃). ¹³ C NMR ∂: 109.9 (s, C(CH₃)₂),76.7, 76.5 (2d, C-2, C-3), 62.2 (t, C-6), 57.8 (d, C-5), 52.1 (d, C-4),50.3 (t, C-1), 27.3 (q, CH₃), 25.6 (q, C(CH₃)₃), 24.8 (q, CH₃), 18.0 (s,C(CH₃)₃), -5.6 (q, SiCH₃). m/z (DCI, NH₃): 361 (M+NH₄ ⁺, 3%), 344 (M+H⁺,1%), 316 (M+H--N₂ ⁺, 100%), 142 (100%). (Found C, 52.36; H, 8.79; N,12.53%. C₁₅ H₂₉ N₃ O₄ Si requires C, 52.47 H, 8.45; N, 12.24%).

EXAMPLE 5 4,5-Anhydro-1-azido-6-O-tert-butyldiphenylsilyl-1-deoxy-2,3-O-isopropylidene-D-talitol (8)

To the epoxy alcohol (6) (0.6 g, 2.62 mmol) in freshly distilled, dryN,N-dimethylformamide (10 ml) was added recrystallised imidazole (0.5 g,7.86 mmol) and tert-butyldiphenylsilyl chloride (1 ml, 3.93 mmol). Thereaction mixture was then stirred at room temperature for 12 hours bywhich time no starting material remained (R_(f) 0.3) and one product wasformed (R_(f) 0.9) by t.l.c. (50%, ethyl acetate/hexane). Removal of thesolvent in vacuo followed by flash chromatography (0-20%, ethylacetate/hexane) then gave4,5-anhydro-1-azido-6-O-tert-butyldiphenylsily-1-deoxy-2,3-O-isopropylidene-D-talitol (8), as a colourless oil (1.5 g, >100%)contaminated with tert-butyldiphenylsilyl alcohol. [α]_(D) ²⁰ +34.1° (c,0.46 in CHCl₃). υ_(max) : 3400, 3000, 2106 cm⁻¹. ¹ H NMR ∂:7.67 (4H, mArH), 7.42 (6H, m, ArH), 4.40 (1H, m, H-2), 3.94 (1H, dd, H-6), 3.85(1H, t, H-3), 3.74 (1H, dd, H-6'), 3.56 (2H, m, H-1, H-1'), 3.12 (1H,quin., H-5), 3.05 (1H, dd, H-4), 1.53, 1.38 (6H, 2s, CH₃), 1.06 (9H, s,C(CH₃)₃). ³ C NMR ∂: 135.8, 133.0, 129.9, 127.9 (Ar), 110.0 (s,C(CH₃)₂), 76.8, 76.6 (2d, C-2, C-3), 62.8 (t, C-6), 57.7 (d, C-5), 52.2(d, C-4), 27.4 (q, CH₃), 26.6 (q, C(CH₃)₃), 24.9 (q, CH₃). m/z (DCI,NH₃): 485 (M+NH₄ ⁺, 10%), 440 (M+H--N₂ ⁺, 75%), 142 (100%). (Found C,64.29; H, 7.37; N, 8.61%. C₂₅ H₃₃ N₃ O₄ Si requires C, 64.23; H, 7.07;N, 8.99%).

EXAMPLE 6 1,4-dideoxy-1,4-imino-2,3-O-isopropylidene-D-mannitol (13)

The epoxide (6) (1.8 g, 8.4 mmol) was stirred in 1,4 -dioxane:water(1:1, 20 ml) under hydrogen in the presence of 10% palladium on carbon(100 mg) for 18 hours by which time no starting material (R_(f) 0.25)remained by t.l.c. (50%, ethyl acetate/hexane). Filtration andevaporation then gave the crude aminodiol which was purified by ionexchange chromatorgraphy to give1,4-dideoxy-1,4-imino-2,3-O-isopropylidene-D-mannitol (13), as an oilwhich crystallised on standing (1.55 g, 90%). This was shown to beidentical to authentic material. m.p. 86°-88° C. (lit. 86°-88° C.)

EXAMPLE 7 1,4-Dideoxy-1,4-imino-D-mannitol (2)

The diol (13) (500 mg, 2.46 mmol) was dissolved in trifluoroaceticacid:water (9:1, 0.5 ml) and stirred for 48 hours at room temperature.Removal of the solvent in vacuo and purification by ion exchangechromatography then gave 1,4-dideoxy-1,4-imino-D-mannitol (2), (33 mg,73%) as a hygroscopic white solid. The hydrochloride salt was thenprepared by addition of dilute hydrochloric acid to an aqueous solutionof the free amine. The salt was then freeze dried before beingrecrystallised. m.p. 149°-151° C. (methanol/diethyl ether) (lit.148°-149° C.).

EXAMPLE 84,5-Anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-6-O-trifluoromethanesulphonyl-D-talitol(9)

To a solution of the epoxy alcohol (6) (1.9 g, 8.6 mmol) in freshlydistilled, dry dichloromethane (40 ml) at -30° C. was added dry pyridine(1.4 ml, 17.2 mmol) followed by trifluoromethanesulphonic anhydride (2.2ml, 13 mmol). The reaction mixture was then stirred for 15 minutes atthis temperature by which time t.l.c. showed no starting material (R_(f)0.25) and one product (R_(f) 0.85). The solution was then washed withdilute aqueous hydrochloric acid (10 ml), saturated copper (II) sulphatesolution (10 ml) and brine (20 ml) before being dried (sodium sulphate).Removal of the solvent in vacuo then gave4,5-anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-6-O-trifluoromethanesulphonyl-D-talitol(9), as a yellow oil which was used immediately without furtherpurification. ¹ H NMR ∂: 4.82 (1H, dd, H-6), 4.40 (2H, m, H-2, H-6'),3.88 (1H, t, H-3), 3.55 (2H, dd, H-1, H-1'), 3.31 (1H, dt, H-5), 3.1(1H, dd, H-4), 1.52, 1.38 (6H, 2s, CH₃). ¹³ C NMR ∂: 110.0 (s, C(CH₃)₂),76.2 (d, C-2), 75.9 (d, C-3), 75.2 (t, C-6), 53.1 (2d, C-4, C-5), 49.9(t, C-1), 27.0, 24.5 (2q, CH₃).

EXAMPLE 9tert-Butyl-8-azido-4,5-anhydro-6,7-O-isopropylidene-2,3,8-trideoxy-L-altro-octanonoate(14)

To the triflate (9) in freshly distilled, dry tetrahydrofuran (15 ml)was added, all at once, lithium tert-butyl acetate (1.6 g, 13 mmol). Thereaction was then stirred for 15 minutes by which time t.l.c. (20%,ethyl acetate/hexane) showed no starting material (R_(f) 0.4) and oneproduct (R_(f) 0.3). Preadsorption and flash chromatography (0-25%,ethyl acetate/hexane) then gave tert-butyl-8-azido-4,5-anhydro-6,7-O-isopropylidene-2,3,8-trideoxy-L-altro-octanonoate(14), as a colourless oil (1.7 g, 60% over three steps). [α]_(D) ²⁰+63.5° (c, 0.95 in CHCl₃). υ_(max) : 2150, 1760 cm⁻¹. ¹ H NMR ∂: 4.37(1H, dt, H-7), 3.75 (1H, dd, H-6), 3.55 (2H, t, H-8 , H-8'), 2.95 (1H,ddd, H-4), 2.84 (1H, dd, H-5), 2.37 (2H, t, H-3, H-3'), 2.03 (1H, m,H-2), 1.77 (1H, p, H-2'), 1.53 (3H, s, CH₃), 1.45 (9H, s, ^(t) Bu), 1.36(3H, s, CH₃). ¹³ C NMR ∂: 172.0 (s, CO), 110.0 (s, C(CH₃)₂), 80.6 (s,C(CH₃)₃), 77.1, 76.6 (2d, C-6, C-7), 57.1 (d, C-5), 55.0 (d, C-4), 50.4(t, C-8), 31.3 (t, C-2), 27.9 (s, CH₃)₃), 27.3, 24.8 (2q, CH₃), 26.5 (t,C-3). m/z (DCI, NH₃): 345 (M+NH₄ ⁺, 15%), 328 (M+H⁺, 5%), 300 (M+H--N₂⁺, 20%), 244 (M+NH₄ --CO₂ ^(t) Bu⁺, 100%). (Found C, 54.98; H, 7.67; N,12.56%. C₁₅ H₂₅ N₃ O₅ requires C, 55.0; H, 7.65; N, 12.84%).

EXAMPLE 10tert-Butyl-5,8-imino-6,7-O-isopropylidene-2,3,5,8-tetradeoxy-D-manno-octanonoate(16)

The azidoepoxide (14) (800 mg, 2.4 mmol) was stirred in ethanol (20 ml)under hydrogen with 10% palladium on carbon (60 mg) for 16 hours. Thecatalyst was then filtered off and the solvent removed in vacuo.Purification by flash chromatography (0-2%, methanol/chloroform) thenaffordedtert-butyl-5,8-imino-6,7-O-isopropylidene-2,3,5,8-tetradeoxy-D-manno-octanonoate(16), as a colourless oil (575 mg, 80%). [α]_(D) ²⁰ -23.8° (c, 0.13 inCHCl₃). υ_(max) : 3400 (broad), 1719 cm⁻¹. ¹ H NMR ∂:4.73 (2H, m, H-6,H-7), 3.87 (1H, s, NH), 3.16 (1H, d, H-4), 2.9 (1H, broad d, OH),2.86-2.35 (5H, m, H-2, H-2', H-5, H-8, H-8'), 1.94 (2H, m, H-3, H-3' ),1.47 (3H, s, CH₃), 1.45 (9H, s, (CH₃)₃), 1.31 (3H, s, CH₃). ¹³ C NMR ∂:173.0 (s, CO), 110.9 (s, C(CH₃)₂), 82.1 (2d, C-6, C-7), 80.2 (s,C(CH₃)₃), 70.6 (d, C-4), 66.5 (d, C-5), 52.3 (t, C-8), 32.0 (t, C-2),30.4 (t, C-3), 27.8 (q, (CH₃)₃), 25.4, 23.3 (2q, CH₃). m/z (CI, NH₃):302 (M+H⁺, 80%), 228 (M-O^(t) Bu⁺, 100%).

EXAMPLE 11(1S,2R,8R,8aR)-1,2-O-Isopropylidene-1,2,8-trihydroxyindolizidin-5-one(17)

The aminoester (16) (0.82 g, 2.7 mmol) was stirred in freshly distilled,dry methanol (25 ml) under reflux with sodium methoxide (10 mg) for 18hours. The solvent was then removed in vacuo and the residue examined byinfrared spectroscopy which showed no ester band (1719 cm⁻¹) and astrong lactam band (1640 cm⁻¹). Filtration through celite with ethylacetate then afforded(1S,2R,8R,8aR)-1,2-O-isopropylidene-1,2,8-trihydroxyindolizidin-5-one(17), as a pale yellow solid which was recrystallised to give a whitesolid (570 mg, 92%). m.p. 126°-128° C. (diethyl ether) (lit:-125°-127°C). [α]_(D) ²⁰ +10.2° (c, 0.39 in methanol). υ_(max) (CHCl₃): 3400(broad), 1640 cm⁻¹. 1 H NMR ∂: 4.80-4.70 (2H, m, H-1, H-2), 4.20 (1H, d,H-8), 4.14 (1H, m, H-8a), 3.33 (1H, dd, H-3), 3.14 (1H, dd, H-3), 3.14(1H, dd, H-3'), 2.60-2.40 (2H, m, H-6, H-6'), 2.15 (1H, m, H-7), 1.89(1H, m, H-7'), 1.42, 1.32 (6H, 2s, CH₃). ¹³ C NMR ∂: 169.0 (s, CO),111.9 (s, C(CH₃)₂), 79.6 (d, C-2), 77.4 (d, C-1), 66.2 (d, C-8), 64.0(d, C-8a), 50.5 (t, C-3), 29.4 (t, C-7), 26.1, 24.4 (2q, CH₃). m/z (CI,NH₃):228 (M+H⁺, 50%). (Found C, 58.25; H, 7.79; N, 6.09%. C₁₁ H₁₇ NO₄requires C, 58.15; H, 7.48; N, 6.17%).

EXAMPLE 12(1S,2R,8R,8aR)-1,2-O-Isopropylidene-1,2,8-trihydroxyindolizidine borane(18)

To the lactam (17) (570 mg, 2.5 mmol) in freshly distilled, drytetrahydrofuran (15 ml) was added, all at once borane:dimethyl sulphidecomplex (1.3 ml, 7.5 mmol). The reaction was then stirred at roomtemperature for 18 hours. Methanol was then added cautiously and thereaction mixture preadsorbed onto silica gel and purification by flashchromatography (0-40%, ethyl acetate/hexane) to give(1S,2R,8R,8aR)-1,2O-Isopropylidene-1,2,8-trihydroxyindolizidine borane(18), as a colourless oil (400 mg, 70%). υ_(max) : 3500 (broad) cm⁻¹. ¹H NMR ∂: 5.27 (1H, t, H-1), 5.06 (1H, dt, H-2), 3.85 (1H, dq, H-8), 3.44(1H, d, H-8a), 3.32 (1H, dd, H-3), 3.23 (1H, dd, H-3'), 3.17 (1H, m,H-5), 3.04 (1 H, m, H-5'), 2.10 (1H, m, H-7), 1.92 (1H, m, H-7'), 1.74(1H, m, H-6), 1.57 (1H, m, H-6'), 1.56, 1.39 (6H, 2s, CH₃). ¹³ C NMR ∂:114.6 (s, C(CH₃)₂), 81.2 (d, C-1), 78.5 (d, C-2), 71.0 (d, C-8), 65.1(d, C-8a), 61.6 (t, C-3), 56.3 (t, C-5), 29.0 (t, C-7), 25.3, 23.5 (2q,CH₃), 18.1 (t, C-6). m/z (CI, NH₃): 228 (M+H⁺, 40%), 214 (M+H--BH₃ ⁺,100%).

EXAMPLE 13 Swainsonine [(1S, 2R, 8R,8aR)-1,2,8-Trihydroxyindolizidine](1)

The aminoborane complex (18) (250 mg, 1.1 mmol) was stirred intrifluoracetic acid:water (1:1, 6 ml) for 48 hours. Removal of thesolvent in vacuo and purification by ion exchange chromatography thengave swainsonine (1) as a white crystalline solid (160 mg, 86%). m.p.141°-143° C. (lit. 141°-143° C.). [α]_(D) ²⁰ -80.3° (c, 0.58 inmethanol), (lit. -78° to -88°). υ_(max) (KBr): 3500 cm⁻¹. 1 H NMR (D₂ O)∂4.14 (1H, m, H-2), 4.05 (1H, dd, H-1), 3.60 (1H, ddd, H-8), 2.74 (2H,m, H-3, H-5), 2.35 (1H, dd, H-3'), 1.89-0.96 (6H, m, 5'-H, H-6, H-6',H-7, H- 7'H-8a). ¹³ C NMR ∂73.1, 69.7, 69.3, (3d, C-1, C-2, C-8), 66.6(d, C-8a), 60.8, 51.9 (2t, C-3, C-5), 32.6 (t, C-7), 23.3 (t, C-6). m/z(DCI, NH₃): 174 (M+H⁺, 100%), 156 (M+H--H₂ O⁺, 15%). This material wasidentical to an authentic sample of swainsonine.

EXAMPLE 143,4-Anhydro-2,7-dideoxy-5,6-O-isopropylidene-L-altro-heptononitrile (15)

To the epoxytriflate (9), prepared from the diol mesylate (12) (1 g, 3.0mmol), in freshly distilled, dry tetrahydrofuran (15 ml) chilled to 0°C. was added all at once, lithium cyanide (150 mg, 4.5 mmol). Thereaction was then stirred for 1 hour at this temperature by which timet.l.c. (20%, ethyl acetate/hexane) showed no starting material (R_(f)0.4) and one product (R_(f) 0.35). Addition of silica gel, removal ofthe solvent in vacuo and purification by flash chromatography (0-20%,ethyl acetate/hexane) then gave3,4-anhydro-2,7-dideoxy-5,6-O-isopropylidene -L-altro-heptononitrile(15), as a colourless oil (560 mg, 77% over 3 steps). υ_(max) (CHCl₃):3500, 2256, 2100. ¹ H NMR ∂: 4.42 (1H, dt, H-6), 3.86 (1H, t, H-5), 3.57(2H, ABX, H-7, H-7'), 3.22 (1H, m, H-3), 3.10 (1H, dd, H-4), 2.82 (2H,ABX, H-2, H-2'), 1.54, 1.38 (6H, 2s, CH₃). ¹³ C NMR ∂: 118.76 (s, CN),110.0 (s, C(CH₃)₂), 76.2 (d, C-6), 76.0 (d, C-5), 54.8 (d, C-3), 51.5(d, C-4), 50.2 (t, C-7), 27.2, 24.7 (2q, CH₃), 20.3 (t, C-2). m/z (CI,NH₃): 256 (M+NH₄ ⁺, 45%), 239 (M+H⁺, 15%), 211 (M+H-28⁺, 100%).

EXAMPLE 154,7-Imino-5,6-O-isopropylidene-2,4,7-trideoxy-D-manno-heptononitrile(19)

The azidocyanoepoxide (15) (560 mg, 2.4 mmol) was taken up in ethanol(15 ml) and stirred under hydrogen in the presence of 10% palladium oncarbon (70 mg) for 12 hours. Filtration, removal of the solvent in vacuoand purification by flash chromatography (0-5%, methanol/chloroform)then gave one major product as a solid (360 mg, 73%) which wasrecrystallised to give4,7-imino-5,6-O-isopropylidene-2,4,7-trideoxy-D-manno-heptononitrile(19), as a white crystalline solid. m.p. 91°-92° C. (ethylacetate/hexane). [α]_(D) ²⁰ -77.2° (c, 0.32 in CHCl₃). υ_(max) (KBr):3400 (broad), 2250 cm⁻¹. ¹ H NMR ∂: 4.76 (2H, m, H-5, H-6), 4.23 (1H, q,H-3), 3.18 (1H, d, H-4), 2.79 (3H, H-2, H-7, H-7'), 2.68 (1H, q, H-2'),1.48, 1.33 (6H, 2s, CH₃). ¹³ H NMR ∂: 118.04 (s, CN), 111.28 (s,C(CH₃)₂), 81.99, 81.84 (2d, C-5, C-6), 66.72 (d, C-3), 66.28 (d, C-4),52.58 (t, C-7), 24.54 (q, CH₃), 24.41 (t, C-2), 23.51 (q, CH₃). m/z (CI,NH₃): 213 (M+H⁺, 100%), 195 (M+H-18⁺, 40%), 142 (M-CHOHCH₂ CN⁺, 25%).(Found C, 57.20; H 7.26; N 13.05%. C₁₀ H₁₆ N₂ O₃ requires C, 56.9; H,7.54; N, 13.27%).

EXAMPLE 16N-Benzyloxycarbonyl-4,7-imino-5,6-O-isopropylidene-2,4,7-trideoxy-D-manno-heptononitrile(20)

To the amine (19) (1.4 g, 6.6 mmol) in a vigorously stirred mixture ofethyl acetate:saturated sodium hydrogen carbonate solution (3:2, 25 ml)was added benzyl chloroformate (1.6 ml, 10 mmol). After 3 hours t.l.c.(50%, ethyl acetate/hexane) showed no starting material (R_(f) 0.0),benzyl alcohol (R_(f) 0.7) and one product (R_(f) 0.6). Separation ofthe organic layer and extraction of the aqueous layer with ethyl acetate(2×15 ml) followed by washing of the combined organics with brine (40ml) and drying (sodium sulphate) gave, after evaporation, the crudeproduct which was preadsorbed and purified by flash chromatography(0-50%, ethyl acetate/hexane) to giveN-benzyloxycarbonyl-4,7-imino-5,6-O-isopropylidene-2,4,7-trideoxy-D-manno-heptononitrile(20), as a white solid (2 g, 88%). m.p. 100°-101° C. (ethylacetate/hexane). [α]_(D) ²⁰ -29.3° (c 0.47 in CHCl₃). υ_(max) : 3350,2251, 1672 cm⁻¹. ¹ H NMR ∂: 7.40 (5H, m ArH), 5.15 (2H, q, PhCH₂), 4.87(1H, t, H-5), 4.77 (1H, q, H-6 ), 4.24 (1H, s, H-3), 4.10 (1H, dd, H-7),3.9 (1H, s, H-4), 3.50 (1H, m, H-7'), 2.73 (1H, dd, H-2), 2.52 (1H, dd,H-2'), 1.55, 1.36 (6H, 2s, CH₃). ¹³ C NMR ∂: 136.0, 128.0 (Ar), 113.7(s, C(CH₃)₂), 80.12, 79.9, 77.8, 77.6, (4d, C-3, C-4, C-5, C-6), 68.0,67.7 (2d, C-7, PhCH₂), 26.1, 24.2 (2q,CH₃), 23.0 (t, C-2). m/z (DCI,NH₃): 364 (M+NH₄ ⁺, 25%), 347 (M+H⁺, 95%), 303 (M--H₂ O--CN⁺, 100%), 213(M+2H--CO₂ CH₂ Ph⁺, 55%), 91 (CH₂ Ph⁺, 90%). (Found C, 62.55; H, 6.50;N, 8.26%. C₁₈ H₂₂ N₂ O₅ requires C, 62.4; H, 6.36; N, 8.09%).

EXAMPLE 17N-Benzyloxycarbonyl-4,7-imino-5,6-O-isopropylidene-2,4,7-trideoxy-D-manno-heptonamide(21)

The cyanide (20) (1.2 g, 3.5 mmol) was stirred for 3 days in methanol(20 ml) with sodium carbonate (220 mg, 2.6 mmol), hexene (4.1 ml, 31.5mmol) and 30% hydrogen peroxide (3.8 ml, 33.4 mmol). Saturated sodiummetabisulphite solution was then added slowly and the reaction mixtureextracted with ethyl acetate (3×30 ml). The combined organic extractswere then washed with brine (70 ml) before being dried (sodiumsulphate). Removal of the solvent in vacuo followed by purification byflash chromatography (0-100%, ethyl acetate/hexane) then gaveN-benzyloxycarbonyl-4,7-imino-5,6-O-isopropylidene-2,4,7-trideoxy-D-manno-heptonamide(21), as a white solid (1.2 g, 94%). m.p. 102°-103° C. (ethylacetate/hexane). v -18.5° (c, 0.66 in CHCl₃). υ_(max) : 3400 broad,1710-1780 cm⁻¹. ¹ H NMR ∂: 7.40 (5H, m, ArH), 5.3 (1H, Bs, NH), 5.12(2H, q, CH₂), 4.87 (1H, t, H-5), 4.75 (1H, m, H-6), 4.36 (1H, m, H-3),4.12 (1H, t, H-4), 4.00 (1H, s, H-7), 3.40 (1H, m, H-7'), 250-2.30 (2H,m, H-2, H-2'), 1.57, 1.35 (6H, 2s, CH₃). ¹³ C NMR ∂ 174.0 (s, CO),136.0, 128.0 (Ar), 113.7 (s, C(CH₃)₂), 80.0, 77.7 (3d, C-3, C-5, C-6),67.9 (d, C-4), 67.6 (t, PhCH₂), 51.0 (t, C-7), 40.0 (t, C-2), 26.1, 24.4(2q, CH₃). m/z (DCI NH₃): 365 (M+H⁺, 100%), 91 (PhCH₂ ⁺, 80%). (Found C,59.49; H, 6.90; N, 7.81%. C₁₈ H₂₄ N₂ O₆ requires C, 59.34; H, 6.59; N,7.69%).

EXAMPLE 18N-Benzyloxycarbonyl-3-O-tert-butyldimethylsilyl-4,7-imino-5,6-O-isopropylidene-2,4,7-trideoxy-D-manno-heptonamide(22)

To the alcohol (21) (374 mg, 1.02 mmol) in dry, freshly distilled,dichloromethane (15 ml) was added dry pyridine (0.55 ml, 6.12 mmol) andtert-butyldimethylsilyl trifluoromethanesulfonate (0.94 ml, 4.08 mmol).The reaction was then stirred for 3 hours at room temperature by whichtime t.l.c. (50%, ethyl acetate/hexane) showed no starting material(R_(f) 0.0) and one product (R_(f) 0.3). The solution was then washedwith dilute aqueous hydrochloric acid (10 ml) then brine (10 ml) anddried (sodium sulphate). Removal of the solvent in vacuo andpurification of the residue by flash chromatography (0-90%, ethylacetate/hexane) then gaveN-benzyloxycarbonyl-3-O-tert-butyldimethylsilyl-4,7-imino-5,6-O-isopropylidene-2,4,7-trideoxy-D-manno-heptonamide(22), as a white solid (480 mg, 98%). m.p. 121°-122° C. (hexane/ethylacetate). [α]_(D) ²⁰ -28.8° (c, 0.53 in CHCl₃). υ_(max) (KBr): 3447,3356, 1684 cm⁻¹. ¹ H NMR ∂: 7.40 (5H, m, ArH), 5.70 (1H, s, NH), 5.11(3H, PhCH₂, NH), 4.79 (1H, t, H-5), 4.70 (1H, q, H-6), 4.59 (1H, q,H-3), 4.16 (1H, t, H-4), 4.01 (1H, dd, H-7), 3.16 (1H, dd, H-7'), 2.61(1H, dd, H-2), 2.39 (1H, dd, H-2'), 1.54, 1.33 (6H, 2s, CH₃), 0.88 (9H,s, C(CH₃)₃), 0.09 (6H, s, CH₃). ¹³ C NMR ∂: 173 (s, CO), 136.0 (Ar),128.0 (s, Ar), 113.0 (s, C(CH₃)₂), 79.6, 77.9 (2d, C-5, C-6), 68.0 (d,C-3), 67.1 (t, PhCH₂ ), 63.5 (d, C-4), 50.9 (t, C-7), 40.9 (t, C-2),27.0 (q, CH₃), 25.7 (q, C(CH₃)₃), 25.0 (q, CH₃), 17.8 (s, C(CH₃)₃),-4.7, -5.1 (2q, SiCH₃). m/z (DCI, NH₃): 479 (M+H⁺, 100%), 421 (M+H--CH₂CONH₂ ⁺, 25%), 345 (M+2H--CO₂ CH₂ Ph⁺, 80%), 328 (M+2H--CO₂ CH₂ Ph--NH₃⁺, 50%), 91 (CH₂ Ph⁺, 70%). Found C, 60.50; H, 8.37; N, 6.19%. C₂₄ H₃₈N₂ O₆ Si requires C, 60.30; H, 7.95; N, 5.86%).

EXAMPLE 193-O-tert-Butyldimethylsilyl-4,7-imino-5,6-O-isopropylidene-2,4,7-trideoxy-D-manno-heptonamide(23)

The protected amine (22) (360 mg, 0.75 mmol) was stirred in ethanol (15ml) in the presence of 10% palladium on carbon (70 mg) under hydrogenfor 1 hour by which time no starting material (R_(f) 0.75) remained byt.l.c. (70%, ethyl acetate/hexane). Filtration and removal of thesolvent then gave3-O-tert-butyldimethylsilyl-4,7-imino-5,6-O-isopropylidene-2,4,7-trideoxy-D-manno-heptonamide(23), as a white solid (235 mg, 91%). m.p. 143°-144° C. (ethyl acetate).[α]_(D) ²⁰ -55.0° (c, 0.26 in CHCl₃). υ_(max) (KBr): 3400 (broad), 1678cm⁻¹. ¹ H NMR ∂: 6.5, 5.8 (2H, 2Bs, NH₂), 4.59 (2H, m, H-3, H-2), 4.26(1H, dt, H-5), 3.04 (1H, d, H-1), 2.75-2.47 (4H, H-6, H-6', H-4, H-1'),1.41, 1.25 (6H, 2s, CH₃), 0.86 (9H, s, C(CH₃)₃), 0.10 (6H, s, Si(CH₃)₂).¹³ C NMR ∂: 173.5 (s, CO), 110.3 (s, C(CH₃)₂), 81.3, 80.1 (2d, C-3,C-2), 67.8 (d, C-5), 67.4 (d, C-4), 53.0 (t, C-1), 42.2 (t, C-6), 25.6(q, (CH₃)₃), 23.3 (q, CH₃), 17.8 (s, C(CH₃)₃), -4.9, -5.3 (2q, SiCH₃).m/z (DCI, NH₃): 345 (M+H⁺, 100%), 328 (M+H--NH₃ ⁺, 35%).

EXAMPLE 20(1S,2R,7R,7aR)-7-O-tert-Butyldimethylsilyl-1,2-O-isopropylidene-1,2,7-trihydroxypyrrolizidin-5-one(24).

The aminoamide (23) (225 mg, 0.65 mmol) was stirred at 80° C. for 1 hourin carbon tetrachloride (8 ml) with sodium hydrogen carbonate (15 mg).T.l.c. (20%, methanol/chloroform) then showed that no starting material(R_(f) 0.2) remained and one product (R_(f) 0.95) had been formed. Thereaction mixture was then filtered and the solvent removed in vacuo.Recrystallisation of the residue gave(1S,2R,7R,7aR)-7-O-tert-butyldimethylsilyl-1,2-O-isopropylidene-1,2,7-trihydroxypyrrolizidin-5-one (24), as a white crystalline solid (195 mg, 92%).m.p. 106°-109° C. (hexane). [α]_(D) ²⁰ -27.2° (c, 0.54 in CHCl₃).υ_(max) : 1690 cm⁻¹. ¹ H NMR ∂: 4.79 (1H, t, H-1), 4.62 (2H, m, H-2,H-7), 3.94 (1H, d, H-3), 3.64 (1 H, dd, H-7a), 2.98 (1H, ddd, H-3'),2.77 (1H, dd, H-6), 2.54 (1H, ddd, H-6'), 1.38, 1.29 (6H, 2s, CH₃), 0.91(9H, s, C(CH₃)₃), 0.11 (6H, s, SiCH₃). ¹³ C NMR ∂: 174.9 (s,CO), 112.1(s, C(CH₃)₂), 81.9, 78.3 (2d, C-1, C-2), 73.0 (d, C-7), 65.1 (d, C-7a),48.2 (t, C-3), 44.0 (t, C-6), 26.1 (q, CH₃), 25.5 (q, C(CH₃)₃), 24.0 (q,CH₃), 17.7 (s, C(CH₃)₃), -5.05, -5.16 (2q, SiCH₃). m/z (DCI, NH₃): 328(M+H⁺, 100%). (Found C, 58.68; H, 9.18; N, 4.13%. C₁₆ H₂₉ NO₄ Sirequires C, 58.7; H, 8.87; N, 4.28%).

EXAMPLE 21(1S,2R,7R,7aR)-7-O-tert-Butyldimethylsilyl-1,2-O-isopropylidene-1,2,7-trihydroxypyrrolizidineborane (26)

To the lactam (24) (270 mg, 0.83 mmol) in freshly distilled, dry,tetrahydrofuran (8 ml) was added a tetrahydrofuran solution ofdiborane/dimethylsulphide complex (0.42 ml, 4.2 mmol). The reaction wasthen left for 12 hours at room temperature before being quenchedcarefully with methanol. Preadsorption and purification by flashchromatography (0-15%, ethyl acetate/hexane) then gave(1S,2R,7R,7aR)-7-O-tert-butyldimethylsilyl-1,2-O-isopropylidene-1,2,7-trihydroxypyrrolizidine (26), as a colourless oil (170 mg, 70%). υ_(max) (CHCl₃):2400 cm⁻¹. ¹ H NMR ∂: 4.97 (1H, q, H-2), 4.84 (1H, t, H-1), 4.67 (1H,quin, H-7), 3.71 (1H, dd, H-3), 3.49 (2H, m, H-3', H-7a), 3.15 (1H, m,H-5), 2.89 (1H, dd, H-5'), 2.28-2.02 (2H, m, H-6, H-6'), 1.50, 1.33 (6H,2s, CH₃), 0.90 (9H, s, C(CH₃)₃), 0.09 (6H, s, SiCH₃). ¹³ C NMR ∂: 113(s, C(CH₃)₂), 82.5, 79.9 (2d, C-1, C-2), 79.5 (d, C-7), 71.8 (d, C-7a)64.6 (t, C-3), 61.2 (t, C-5), 34.9 (t, C-6), 27.0 (q, CH₃), 25.5 (q,C(CH₃)₃), 24.6 (q, CH₃), 17.6 (s, C(CH₃)₃), -5.03, -5.14 (2q, SiCH₃).

EXAMPLE 22 (1S,2R,7R,7aR)-1,2,7-Trihydroxypyrrolizidine (3)

The borane adduct (26) (170 mg, 0.52 mmol) was dissolved intrifluoroacetic acid: water (1:1, 4 ml) and stirred for 24 hours at roomtemperature. Removal of the solvent in vacuo and purification by ionexchange chromatography with Dowex 50(H) followed by AmberliteCG-400(Cl) resins then gave (1S,2R,7R,7aR)-1,2,7-trihydroxypyrrolizidine(3), as a gum which was recrystallised to give a white solid (57 mg,68%). m.p. 150°-153° C. (ethanol). [α]_(D) ²⁰ -29.3° (c, 0.15 in MeOH).υ_(max) (KBr): 3400, 3270 cm⁻¹. ¹ H NMR (D₂ O)∂: 4.40 (1H, q, H-7), 4.04(1H, m, H-2), 3.98 (1H, q, H-1), 3.08 (1H, t, H-7a), 2.94 (2H, m, H-3,H-5), 2.48 (1H, m, H-5'), 2.33 (1H, t, H-3'), 2.01 (1H, s, H-6), 1.62(1H, m, H-6'). ¹³ C NMR ∂: 73.7, 73.1 (2d, C-1, C-2), 70.9 (d, C-7),70.6 (d, C-7a), 56.0 (t, C-3), 53.5 (t, C-5), 34.8 (t, C-6). m/z (DCI,NH₃): 160 (M+H⁺, 35%). (Found C, 52.79; H, 8.33; N, 8.53%. C₇ H₁₃ NO₃requires C, 52.83; H, 8.18; N, 8.81%).

EXAMPLE 23(1S,2R,7R,7aR)-1,2-O-Isopropylidene-1,2,7-trihydroxypyrrolizidin-5-one(25)

To the silyl alcohol (24) (130 mg, 0.38 mmol) in freshly distilled drytetrahydrofuran (5 ml) was added tetrabutylammonium fluoride intetrahydrofuran (0.76 ml, 0.76 mmol). The solution was then stirred for2 hours at room temperature. T.l.c. (10%, methanol/ethyl acetate) thenshowed no starting material (R_(f) 0.9) and one product (R_(f) 0.4).Preadsorption and purification by flash chromatography (0-10%,methanol/ethyl acetate) then gave (1S,2R,7R,7aR)-1,2-O-isopropylidene-1,2,7-trihydroxypyrrolizidin-5-one (25), as a white solid (84 mg,100%). m.p. 148°-149° C. (ethyl acetate). [α]_(D) ²⁰ 0° (c, 0.305 inCHCl₃). υ_(max) : 3360, 1669 cm⁻¹. ¹ H NMR ∂: 4.80 (1H, t, H-2), 4.67(2H, m, H-1, H-7), 3.97 (1H, d, H-3), 3.70 (1H, dd, H-7a), 3.00 (1H, dd,H-3'), 2.85 (1H, dd, H-6), 2.58 (1H, ddd, H-6'), 2.50 (1H, t, OH), 1.37,1.28 (6H, 2s, CH₃). ¹³ C NMR ∂: 175.9 (s, CO), 112.1 (s, C(CH₃)₂), 81.8,78.5 (2d, C-1, C-2), 72.7 (d, C-7), 64.4 (d, C-7a), 48.6 (t, C-3), 43.6(t, C-6), 26.1, 23.9 (2s, CH₃). m/z (CI, NH₃): 231 (M+NH₄ ⁺, 20%), 214(M+H⁺, 100%), 198 (M+H--O⁺, 30%), 196 (M+H--H₂ O⁺). (Found C, 56.27; H,6.89; N 6.35%. C₁₀ H₁₅ NO₄ requires C, 56.34; H, 7.04; N, 6.57%).

EXAMPLE 24 (1S, 2R,7aS)-1,2-Dihydroxy-1,2-O-isopropylidenepyrrolizidin-5,7-dione (28)

To the alcohol (25) (77 mg, 0.36 mmol) in freshly distilled drydichloromethane (7 ml) was added pyridinium chlorochromate (155 mg, 0.72mmol) and 4 Å powdered molecular sieve (155 mg). The reaction was thenstirred for 1 hour by which time t.l.c. (10%, methanol/ethyl acetate)showed no starting material (R_(f) 0.4) and one product (R_(f) 0.5).Silica gel was then added and the solvent removed in vacuo. Purificationby flash chromatography (0-10%, methanol/ethyl acetate) then gave (1S,2R, 7aS)-1,2-dihydroxy-1,2-O-isopropylidenepyrrolizidin-5,7-dione (28)slightly contaminated with chromate residues which was used immediately.υ_(max) : 1775, 1698 cm⁻¹. ¹ H NMR ∂: 4.83 (2H, m, H-1, H-2), 4.34 (1H,d, H-3), 4.08 (2H, m, H-3', H-7a), 3.10 (2H, m, H-6, H-6' ), 1.38, 1.26(6H, 2s, CH₃). ¹³ C NMR ∂: 172.1 (s, CO), 112.7 (s, C(CH₃)₂), 81.5, 80.0(2d, C-1, C-2), 72.7 (d, C-7a), 50.3 (t, C-3), 43.4 (t, C-6), 26.0, 23.6(2q, CH₃).

EXAMPLE 25(1S,2R,7S,7aR)-1,2-O-Isopropylidene-1,2,7-trihydroxypyrrolizidin-5-one(29)

To the ketone (28) in ethanol (5 ml) at 0° C. was added sodiumborohydride (30 mg, 0.72 mmol). The reaction was then stirred at 0° C.for 15 minutes by which time t.l.c. (10%, methanol/ethyl acetate) showedno starting material (R_(f) 0.5) and one product (R_(f) 0.4). Thereaction was then quenched with ammonium chloride before beingpreadsorbed onto silica gel and purified by flash chromatography (0-10%,methanol/ethyl acetate) to give(1S,2R,7S,7aR)-1,2-O-isopropylidene-1,2,7-trihydroxypyrrolizidin-5-one(29), as a white crystalline solid (72 mg, 94%). m.p. 132°-134° C.(ethyl acetate). [α]_(D) ²⁰ -19.3° (c, 0.46 in CHCl₃). υ_(max) : 3410,1671 cm⁻¹. ¹ H NMR ∂: 4.79 (3H, m, H-1, H-2, H-7), 4.08 (1H, d, H-3),3.85 (1H, dd, H-7a), 3.58 (1H, d, OH), 2.94 (2H, m, H-3', H-6), 2.40(1H, dd, H-6'), 1.46, 1.31 (6H, 2s, CH₃). ¹³ C NMR ∂: 175.6 (s, CO),112.7 (s, C(CH₃)₂), 82.1, 80.2 (2d, C-1, C-2), 66.8 (d, C-7), 65.5 (d,C-7a) 49.5 (t, C-1), 42.7 (t, C-6), 26.0, 23.9 (2q, CH₃). m/z (CI, NH₃):231 (M+NH₄ ⁺, 15%), 214 (M+H⁺, 100%). (Found C, 56.45; H, 7.16; N,6.34%. C₁₀ H₁₅ NO₄ requires C, 56.3; H, 7.04 N, 6.57%).

EXAMPLE 26(1S,2R,7S,7aR)-1,2-O-Isopropylidene-1,2,7-trihydroxypyrrolizidine borane(27)

To the lactam (29) (70 mg, 0.32 mmol) in freshly distilled, drytetrahydrofuran (8 ml) was added diborane/dimethylsulphide complexsolution (0.1 ml, 0.98 mmol). The reaction was then left for 12 hours atroom temperature before being quenched carefully with methanol.Preadsorption and purification by flash chromatography (0-40%, ethylacetate/hexane) then gave(1S,2R,7S,7aR)-1,2-O-isopropylidene-1,2,7-trihydroxypyrrolizidine borane(27), as a colourless oil (50 mg, 72%). υ_(max) : 3220, 2364 cm⁻¹. ¹ HNMR ∂: 5.01-4.86 (3H, m, H-1, H-2, H-7), 3.67-3.28 (5H, m, H-3, H-3',H-5, H-5', H-7a), 2.64 (1H, m, H-6), 1.93 (1H, m, H-6'), 1.57, 1.35 (6H,2s, CH₃). ¹³ C NMR ∂: 112.1 (s, C(CH₃)₂), 81.7, 80.5 (2d, C-1, C-2),75.9, 72.9 (2d, C-7, C-7a), 66.1, 59.5 (2t, C-3, C-5), 34.9 (t, C-6),25.8, 23.1 (2q, CH₃).

EXAMPLE 27 (1S,2R,7S,7aR)-1,2,7-Trihydroxypyrrolizidine (4)

The borane adduct (27) (50 mg, 0.24 mmol) was dissolved intrifluoroacetic acid: water (1:1, 4 ml) and stirred for 24 hours at roomtemperature. Removal of the solvent in vacuo and purification by ionexchange chromatography with Dowex 50(H) followed by amberliteCG-400(Cl) then gave (1S,2R,7S,7aR)-1,2,7-trihydroxypyrrolizidine (4),as a gum (27 mg, 70%) which crystallised on trituration with diethylether. m.p. 125°-127° C. [α]_(D) ²⁰ -6.9° (c, 0.13 in MeOH). υ_(max)(KBr): 3395, 3269 cm⁻¹. ¹ H NMR (D₂ O)∂: 4.38 (1H, q, H-7, J₁,2 4.2 Hz,J₁,3 8.5 Hz), 4.25 (1H, dd, H-1, J₁,2 1.4 Hz, J₁,3 5.9 Hz), 4.04 (1H, m,H-2), 3.37 (1H, t, H- 7a, J₁,2 5.6 Hz), 3.08 (1H, dd, J₁,2 4.8 Hz, J₁,310.4 Hz), 3.00 (1H, m, H-5), 2.72 (1H, m, H-5'), 2.61 (1H, dd, H-1',J₁,2 2.9 Hz, J₁,3 10.6 Hz), 1.75 (2H, m, H-6, H-6'). ¹³ C NMR ∂: 73.1(d, C-1, C-2), 72.8 (d, C-7), 68.0 (d, C-7a), 57.3 (t, C-3), 53.5 (t,C-5), 35.6 (t, C-6). m/z (DCI, NH₃): 160 (M+H⁺, 40%). (Found C, 52.56;H, 8.69; N, 8.76%. C₇ H₁₃ NO₃ requires C, 52.83; H, 8.18; N, 8.81%).

Various other examples will be apparent to the person skilled in the artafter reading the present disclosure without departing from the spiritand scope of the invention. It is intended that all such other examplesbe included within the scope of the appended claims.

What is claimed is:
 1. A method for the synthesis of1,4-dideoxy-1,4-imino-D-mannitol comprising:a) catalyticallyhydrogenating 4,5-anhydro-1-azido-1-deoxy-2,3-O-isopropylidene-D-talitolto provide ring closure and give a protected pyrrolidine and b) removingthe isopropylidene protecting group in the protected pyrrolidine by acidhydrolysis to give 1,4-dideoxy-1,4-imino-D-mannitol.